Re: Mag623 with 4D Stock switch/4 imr 26650 and 85K lux
My calculation was based on the assumption that all factors remain the same and the throwmaster had an outside diameter of 2.5 inches. As you say, 2.5 inches is actually the inside diameter. This makes a big difference (a little bit more diameter increases the area of a circle significantly).
For throw you need the surface area of the reflector as seen when looking straight at the light from the front (this is reason why the depth doesn't have much effect on center beam throw) and the luminance of the light source. From this number you need to subtract a few things like transmission losses from the lens and the reflectivity of the used reflector.
The calculation is very accurate if the used data is accurate. We have been using it for years in the German TLF forum.
Here is a very good explanation. Just use google translate since it is in German.
Here is is my new calculation:
We need to first calculate the luminance of the bulb, since there is no data for it.
Surface area of standard mag reflector (what is the diameter of the bulb opening of the kaidomain reflector?):
diameter large opening: 47.4mm
diameter small opening: 15.3mm
surface area: (47.4/2 * pi) - (15.3/2 * pi) = 1581mm^2
Surface area of throwmaster reflector:
diameter large opening: 64mm
diameter small opening: 12.5mm
surface area: 3094mm^2
For comparison - surface area of FM3X 3-inch reflector:
diameter large opening: 71.5mm
diameter small opening: 12.5mm
surface area: 3892mm^2
Now the lux numbers from bigchelis make much more sense. The throwmaster should double the lux value of the light.
I don't have more time now. I will finish the calculation later.
EDIT:
The formular for Throw is:
Beam intensity [cd] = reflector surface area [mm^2] * luminance of lightsource [cd/mm^2] * reflector reflectitivity [%] * lens transmission [%]
This is how you calculate the throw
at turn-on. Led light tend to lose brightness because of heat (depends on how good the heat dissipation of the light is). This would be an additional factor for the calculation. Similarily incan lights without regulation lose brightness because the battery voltage drops continiously. Regulated incan lights should be perfectly constant.
I will now use this to calculate the appoximate luminance of the bulb in big_chelis light:
Luminance of bulb = 85,000cd / (1581mm^2 * 0.9 * 0.92) = 65cd/mm^2
Now I will calculate the approximate throw this bulb will produce with the Throwmaster head using the dimensions that fivemega posted:
Beam intensity = 3094mm^2 * 65cd/mm^2 * 0.9 * 0.92 = 166,519cd = 167kcd
Pretty dang close to the measured numbers
.
Like I wrote before - for maximum throw the FM3X-Heads will be better, because they have an even larger diameter.
Beam intensity = 3892mm^2 * 65cd/mm^2 * 0.9 * 0.92 = 209,467cd = 210kcd
@fivemega: for throw only the surface area of the reflector as seen from the front actually counts. Depth does not make a big difference here. The one thing it can influence is the bulb hole diameter. Making it smaller will increase the surface area by a tiny amount. The diameter of the large reflector opening is the only thing that really makes a difference. Please remember though that I am only talking about the throw (center beam candela/lux). Not the shape of the beam or anything like that. For those types of things your deep reflectors seem to make a really big difference.